JOP156 Multi-Spectral Solar Telescope Array III
D. Martinez-Galarce, P. Scherrer, P. Boerner
Coordinated campaign with TRACE, SoHO, the MSSTA rocket, and
ground-based observatories
Received: March 14, 2002
--GOALS--
The Multi-Spectral Solar Telescope Array rocket is scheduled for launch
on 10 April, 2002. The MSSTA is an observatory that uses an array of
multilayer telescopes to probe the structure and dynamics of the solar
atmosphere. The flight configuration consists of 12 telescopes, each
of which will image the full solar disk with spatial resolution of ~1
arc-second. Each instrument's bandpass is tuned to one or more strong
emission lines.
The MSSTA will produce a powerful dataset of high-resolution full-disk
spectroheliograms. The expected dataset is summarized below:
Wavelength Ion T_Formation Resolution
57.9 Mg X 1.0 MK 5 arc-sec
98.3 Ne VIII 0.5 MK 5 arc-sec
131 Fe VIII/Fe XX 0.7MK/8MK 5 arc-sec
150.1 O VI/NiXII/XIII 0.4MK/1.3MK 1 arc-sec
171 Fe IX/X 1 MK 2 arc-sec
180 Fe XI 1.2 MK 2 arc-sec
195 Fe XII 1.5 MK 1 arc-sec
211 Fe XIV 2 MK 1 arc-sec
256 He II 0.08 MK 1 arc-sec
1216 H Ly a 0.02 MK 1 arc-sec
1550 C IV/UV cont 0.1 MK/4000 K 1 arc-sec
(* 93.9 Fe XVIII 6.5 MK 5 arc-sec*)
All images will be recorded on photographic film, allowing the field of
view to span from the center of the solar disk out to 5-15 solar radii.
All will be photometrically calibrated.
While the spectral resolution of the MSSTA telescopes is insufficient
to measure velocities or most line ratios, the MSSTA data will allow
modeling of local and global emission measure as well as
cross-calibration of other EUV observatories (especially TRACE and
EIT).
--PLAN--
TRACE
In order to maximize the utility of the MSSTA data in cross-calibration
with TRACE, we would like full-disk mosaics taken in as many as
possible of TRACE's EUV bandpasses, as well as 1216 and 1550, within a
few hours of flight. During flight, we would like high-cadence 171 Ê
observations of a prominent active region, with images of the same
region in all bandpasses before and after the start of the high-cadence
observations. We would also like a series of deep observations of a
quiet region in multiple bands taken as close to the flight window as
other requirements allow.
EIT:
Full disk images in 304, 284, 171 and 195 before, during and after
flight.
MDI (added by SOHO SOC):
Full disk magnetograms and dopplergrams at a one minute cadence.
Yohkoh:
Full-disk SXT images, or partial-frame images of bright active region.
CDS:
CDS will coordinate with TRACE and perform a raster with good spectral
information over a square region during the flight.
OTHER Observatories:
The dataset's relevance to the chromosphere and photosphere would be
enhanced by obtaining full-disk ground based observations in white
light, H alpha, and Ca K, as well as full-disk magnetograms, as close
to the time of flight as possible.
--PROPERTIES OF MSSTA DATA--
Spatial Resolution:
Using the 3500mm focal length Ritchey-Chretien systems and
high-resolution 649 film, the MSSTA is, in principle, capable of
spatial resolution around 0.3 arc-seconds across the solar disk. The
shorter-focus telescopes and coarser-grained XUV-100 film are still
capable of imaging at around 1 arc-second resolution. Our past
experience with the MSSTA suggests that the low signal-to-noise ratio
at high spatial frequencies limits the useful resolution to a few
(5-10) arc-seconds, although we hope to achieve sub-arc-second
resolution with at least some of the MSSTA instruments.
Spectral Resolution:
The 9 EUV telescopes will have narrowband multiplayer coatings
applied by Troy Barbee of Lawrence Livermore National Labs. The FWHM of
the coating bandpasses varies (tending to increase with higher central
wavelengths), but we expect values ~5 Ê, or E/dE ~ 30. This is
generally sufficient to ensure that the image formed by each telescope
is dominated by a single emission line (and thus that each image shows
the distribution of plasma at a particular temperature). Notable
exceptions are the 131 Ê Herschelian and the 150 Ê Ritchey-Chretien
telescope. These bandpasses are centered on transition region lines (T
~ 400,000 or 600,000 K), but allow for a significant contribution from
lines of highly-ionized nickel or iron on either side of the peak. The
resulting spectroheliogram should be dominated by TR emission over most
of the solar surface, with strong emission from the hot lines appearing
over the active regions. Filtering the two components of the image, by
subtraction of an Fe XII image (Fe XII emission should be highly
correlated with Ni XI and XII emission) for example, may be possible.
The FUV telescope optics and filters were prepared by the Acton
Research Corporation; as a system (both mirror coatings and filters
contribute to narrowing the bandpass) they have E/dE ~ 200. However,
because there is a strong continuum in the neighborhood of the C IV
line, the resulting spectroheliogram will be dominated by the emission
of material much cooler than C IV. We do not have provisions to perform
any continuum subtraction of the sort described by Handy et al for
"purifying" TRACE C IV images.
Time Resolution:
The MSSTA data will more closely resemble portraits than movies.
Because of the relatively modest aperture and low detector QE of the
MSSTA instruments, exposure times of up to 200 seconds will be
necessary to achieve high signal-to-noise spectroheliograms. This
fact, coupled with the limit of ~350 seconds of useful observing time
in flight, makes it difficult to attempt any high-cadence observations.
Energy Calibration:
Detailed calibration of all instruments will not be completed
until after the flight. Based on our experience in calibrating the
MSSTA telescopes and film at SSRL, we expect to be able to provide
absolute flux calibration for all images accurate to ~25%.
Field of View:
The sensitivity of the MSSTA telescopes is sufficient to show some
structure in the extended corona in longer exposures. Unlike in past
MSSTA flights, each instrument will image onto a dedicated camera.
Therefore, the unvignetted field of the telescopes ranges from 15 solar
radii in diameter for the 1000 mm focal-length Herschelian telescopes
to 4 solar radii for the 3500 mm Ritchey-Chretiens. However, the
telescopes are optimized for recording the higher-flux emissions from
on the disk.